Why the fascination with subwoofers?

I have noticed many posts with questions about adding subwoofers to an audio system. Why the fascination with subwoofers? I guess I understand why any audiophile would want to hear more tight bass in their audio system, but why add a subwoofer to an existing audio system when they don’t always perform well, are costly, and are difficult to integrate with the many varied speakers offered. Additionally, why wouldn’t any audiophile first choose a speaker with a well designed bass driver designed, engineered and BUILT INTO that same cabinet? If anyone’s speakers were not giving enough tight bass, why wouldn’t that person sell those speakers and buy a pair that does have tight bass?
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I use 4 subs but I have floor to ceiling linear arrays and two subs just won't make it. If you are clever and work with your room acoustics and you have a point source system which is just about all of you, 2 subs will work perfectly fine. In most normally sized houses I do not see the need for drivers over 12".  I think 12" is perfect. In addition to a properly designed driver the key to sub performance is a very heavy solid enclosure. Any vibration of the enclosure is distortion. If you put your hand on the enclosure at volume and you feel it buzzing away you have a problem. The best enclosures do not resonate at all and you do not have to do anything to them. If your enclosure vibrates the first thing to do is go to the local granite store and you can usually get cut offs for cheap. Just place an appropriately sized piece right on top of the sub. That can help tighten things up quite a bit. Also make sure the sub has 3 spiked feet not four. Three feet make a much better connection to the floor. No rocking. Subs have to be right up against a wall or in a corner. They are 3 to 9 db more efficient this way.
Some people are after All the response , not just down to what their neighbours are ok with. If i had two speakers that incorporated the subs involved they would weigh 250 pounds each . A four way system tri amped is far and few between and i dont think manufacturers are willing to sit on them hoping someone will buy them before some fancy pants gives them a thumbs down. Everything is a seasoned to taste affair . Pick your components and turn your obtainable mains into monsters for a much more realistic concert experience. Or bump them up a little bit in low listening levels to make the sound fuller .
One benefit of of more subs is the ability to run them all lower . Less buzzing . Less distortion . 
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     Subs in corners, since they couple to two walls, typically results in a 3 db+ bass boost.   It sounds like you're making the right moves, keeping your subs way from the corners and controlling the effects of a suspended floor, to keep the bass clean and accurate, detailed, smooth and natural.